Dear Ravnish, one of the reasons is the issue of cost.

- Tunnel Boring Machines cost millions. They take many months (at least 10-12 months I am guessing) to produce. So there is a lead time before you can start the excavation, unlike in Drill & Blast method. Most countries have to import such machinery and they may not have the foreign reserves to afford one. They also require very specialized personnel to operate them.

For a tunnel boring machine to justify its use, the tunnel has to be at least of a certain length. From 2016, somebody had told me that the tunnel had to be at least 4 kilometers long. Otherwise it would not be viable. I suspect the cost must have gone done a bit because of the Chinese TBM producers.

I think there are less and less excuses nowadays not to use TBMs. They are safer for workers to start with.

I totally agree, the most important factor is cost. And in low-length tunnels, this is not affordable. But to complete the discussion, I have a few questions:
Did you start drilling with excavation Tbm from the mouth of the tunnel portal (0 + 000 Tunnel) ?
Certainly the first and last few hundred meters are best excavated in a traditional or semi-mechanized way.
Can a cross-section be created with Tbm other than a circle?
The cross section of many tunnels is not circular. And after drilling most of the tunnel by Tbm, drilling should be done in other ways to complete the final cross-sectional area.
Can it be said that, for each tunnel, tbm alone is not the answer in any case, there is a need for mix  traditional and semi-mechanized drilling alongside tbm

This article provides some solid reasons for preferring the Drill & Blast over the tunnel boring machine boring.

https://tunnelingonline.com/advancements-in-tunneling-and-underground-excavation-by-drill-blast/

"Tunneling by drill-and-blast is still the most common method in the Underground Mining Industry while Tunneling for infrastructure projects is more and more becoming mechanized tunneling by TBM or other methods. However, in short tunnels, for large cross sections, cavern construction, cross-overs, cross passages, shafts, penstocks, etc., Drill and Blast is often the only possible method. By Drill and Blast we also have the possibility to be more flexible to adopt to varying profiles compared to a TBM tunnel that always gives a circular cross section especially for highway tunnels resulting with a lot of over excavation in relation to the actual cross section needed."

@Arash You are right. Cost is not the only reason why you may want to go for non-TBM tunnelling. As you have pointed out there are some other important considerations in favour of conventional tunnelling.